jb42...i am terribly sorry to hear about the EA, but sadly not surprised. as many folks will tell you hear no matter how unique we feel our individual sitches are, basically they aren't. in my sitch while w has not said anything about EA/PA/OM and i've not bothered once to look, her words/actions and my gut tell me there is.
i completely agree your W is just trying to absolve her guilt by saying this started post-BD. feel like my W is fast tracking the D for exactly the same reason. "oh we met after BD/were separated so I wasn't cheating"....yeah right
at least now you know. use that to shift gears so to speak. focus on you and moving yourself forward. if w wants that OM and is willing to lose you, let her be the fool by being strong and letting her go. it's not like you can control her decisions/actions anyway. for sure you will cycle with your emotions, allow yourself to experience what comes, but DO NOT let her see them!
and keep posting here as needed. you are not alone in what you are going through and there is so much good information here that can help you.